Recently, with a progress of gene recombination technology, a wide variety of useful proteins have been successfully produced by use of a microorganism such as Escherichia coli. However, in the case where a foreign-protein gene derived from a eukaryote is expressed in Escherichia coli as a host, it is known that normal posttranslational modification such as normal processing and addition of a sugar chain is not made. This is a problem. For this reason, yeast, which is a eukaryote, is relatively frequently used as a host. As the host yeast, for example, Saccharomyces cerevisiae, Pichia pastoris, Pichia methanolica, Schizosaccharomyces pombe, Hansenula anomala and Kluyveromyces lactis are known (see, for example, patent document 1). However, the expression level of a foreign protein in a yeast used as a host could have been room for improvement.
To express a foreign-protein gene in a host, a recombinant polynucleotide, in which the foreign-protein gene has been placed operably under the control of a promoter capable of functioning in a host, is introduced into the host. In the resultant transformant, the foreign protein is expressed. Since the transcriptional activity of a promoter significantly influences the expression efficiency of the foreign protein, a promoter having a high transcriptional activity is generally used. Furthermore, it is preferable to induce expression of a foreign-protein gene with desired timing. This is because the efficiency for producing a foreign protein increases in fermentative production using a transformant, when the transformant is first allowed to proliferate as much as possible and then a foreign protein is expressed. As an inducible promoter having a high transcriptional activity, a galactose inducible promoter is well known. The galactose inducible promoter refers to a promoter which can be induced by galactose during glucose deficiency time. In Saccharomyces cerevisiae, etc., a promoter (GAL promoter) of a galactose metabolism gene (GAL gene) such as GAL1 promoter, GAL2 promoter, GAL3 promoter, GAL5 promoter, GAL7 promoter and GAL10 promoter, are frequently used (see for example, patent document 2).
In the meantime, Kluyveromyces marxianus is a heat resistant yeast (see for example, non-patent documents 1 and 2). In the case where ethanol fermentation is performed in yeasts generally employed, since fermentation heat raises the temperature of a fermentation liquor, cooling of the fermentation liquor was required in order to continuously perform ethanol fermentation. Therefore, to industrially perform ethanol fermentation, a large-scale cooling facility and tremendously large energy cost for cooling are indispensable. However, Kluyveromyces marxianus, which can proliferate at a temperature as high as 48° C. (non-patent documents 3 and 4), enables efficient ethanol fermentation without requiring such cooling facility and energy cost. The sequence of the GAL promoter of Kluyveromyces marxianus has not yet been elucidated.